In liquid fueled combustors, the fuel is converted to a spray consisting of a system of fuel droplets, and fuel vapor. Such fuel sprays contain numerous individual droplets which can range in size from about 2 microns (.mu.) to about 200.mu.. These droplets must evaporate, and mix with the oxidant, which is generally air, before effective combustion can occur. In attempting to better understand the events which are occurring within these combustors, literally hundreds of theoretical and experimental investigations have been performed concerning a single, isolated droplet as well as the complex, multidroplet sprays.
When liquid fuel is injected into a hot gas atmosphere as in a gas turbine or diesel engine, the atomized droplets evaporate as heat from the surrounding atmosphere is transferred into the interior regions of the spray. The temperature within the individual spray droplets is thus the key parameter in estimating the heat transfer and the vaporization rates Most conventional experimental methods for spray analysis, i.e. photography, laser light scattering, multiphase probes, etc. do not measure droplet temperature. In addition, although present temperature determining apparatuses such as the optical pyrometer and thermocouples, can be of assistance in studying the heat transfer properties of sprays and fluids they are not useful for determining localized temperatures such as for example, in a droplet. Thus, direct measurement of droplet temperatures has not been possible and mathematical equations have been utilized to estimate droplet temperatures. Most often, it is assumed that the droplet temperature rises rapidly and homogeneously at the boiling point of the fuel. However, recent work regarding internal circulation and multicomponent evaporation has called this assumption into question. Given the importance of determining localized fluid temperatures so that the thermal properties of fluids and sprays may be more accurately determined, there is a need for methods of determining the temperatures of fluids, and in particular, droplets.
Accordingly, there has been a constant search in this field of art for methods of determining the temperatures of fluids, particularly dispersed fluids.